The present invention relates to fluid pressure control devices.
A fluid pressure control device can be designed for regulating operation of a hydrostatic transmission system, a hydropump and/or a hydromotor of which system is adjusted by a variable control oil pressure as a function of hydraulic working pressure or rate of delivery of oil in the transmission system.
In such a hydraulic system, it has been proposed to apply the control pressure for adjusting the hydropump and/or the hydromotor of the transmission system, and therewith the power data of the transmission system, either by means of a separate auxiliary pump or by branching off oil from a main oil flow of the transmission system in a predetermined ratio thereto. In such a system a fluid pressure control valve device can effect adjustment, for example for power control of the transmission system, of the control pressure as a function of a predetermined parameter, for example as a function of hydraulic working pressure or oil flow supplied to the hydromotor of the transmission system. Such a control device as hitherto proposed may be unduly costly, since it is either provided with a separate auxiliary pump, for obtaining the control pressure, or else it is very complicated.
Of possible interest also in this respect is German Auslegeschrift No. 1,247,437, in which there is proposed a control valve, employed as a branch valve which, on the one hand, branches off an auxiliary oil stream supplied by an auxiliary oil pump, for replacing leakage oil losses in a transmission system circuit and, on the other hand, supplies a control oil pressure for adjusting a hydropump and/or a hydromotor of a hydraulic transmission system.
The power or working capacity of a hydrostatic transmission system is determined by the product of hydraulic working pressure and main fluid flow in the transmission system. The present invention has accordingly been developed with a view to providing a control device that can be designed to enable power or working capacity of a hydraulic transmission system to be controlled in a relatively simple manner in accordance with a substantially direct, predetermined association between hydraulic working pressure and main fluid flow in such a transmission system.